1. Field of the Invention
The present invention relates to a remaining charge detection device for a power storage unit, such as a battery. More specifically, the present invention relates to a remaining charge detection device for a power storage unit, which utilizes a technique of calibrating the remaining charge calculated based on a current accumulation method.
2. Description of Related Art
As a method for detecting the remaining charge of a power storage unit (e.g., a battery) which is provided in, for instance, a hybrid car, one is generally known in which the accumulated charge amount and the accumulated discharge amount of the battery are calculated by estimating the charging current and the discharging current of the battery for each given period of time, and adding or subtracting the accumulated charge amount/the accumulated discharge amount to/from the initial charge or the remaining charge of the battery prior to the charging-discharging processes, since the remaining charge of the battery corresponds to the total amount of electric charge retained in the battery.
However, in the above-mentioned method, for instance, measurement errors in the current detector accumulate when the accumulated charge amount and the accumulated discharge amount are calculated, and errors contained in the calculated remaining charge may be increased.
Because of the problems described above, as a remaining charge detection device for a battery, which is capable of calibrating the remaining charge calculated based on the above-mentioned current accumulation method to an accurate value at a suitable timing, Japanese Unexamined Patent Application, First Publication No. 10-132911, for instance, discloses a battery remaining charge detector in which predetermined relational expressions or maps for current values, voltage values, and remaining charges for the battery are stored. The battery remaining charge detector calculates the remaining charge of the battery based on the current value and the voltage value of the charging/discharging current of the battery detected by a current detector and a voltage detector, respectively, and carries out a calibration of the calculated remaining charge based on the stored relational expressions or maps.
However, since the predetermined relational expressions or maps retained in the above-mentioned battery remaining charge detector are prepared based on the voltage characteristic of a battery in its stationary state (i.e., the battery has not deteriorated), there is a difference between the actual remaining charge of the battery and the remaining charge of the battery calculated based on the predetermined maps or relational expressions, and the difference may be increased when the internal resistance of the battery is increased by, for instance, the deterioration of the battery. If a value which contains an error is detected as the remaining charge of a battery, the battery may be used exceeding its limit and the life of the battery may be shortened.
Also, when the remaining charge of a battery is defined as a percentage with respect to a predetermined standard charge of the battery and such a percentage value is used for controlling a motor or an engine, problems may arise in controlling the motor or engine and they may not be properly controlled if the degree of deterioration of the battery is not reflected to the standard charge of the battery.
The present invention is achieved in consideration of the above situation, and its objectives include the provision of a remaining charge detection device for a power storage unit, which enables calculation, even if the power storage unit has deteriorated, of an accurate remaining charge thereof based on an accumulated charge amount and an accumulated discharge amount obtained by estimating a charging current and a discharging current.
Accordingly, the present invention provides a remaining charge detection device for a power storage unit (for instance, a battery 14 in an embodiment of the invention which will be described later) including: a current detection unit (for instance, a current detector 26 in an embodiment of the invention which will be described later) which detects the current value of a charging current and a discharging current of a power storage unit; a voltage detection unit (for instance, a voltage detector 28 in an embodiment of the invention which will be described later) which detects the voltage value of a terminal voltage of the power storage unit; and a current accumulation remaining charge calculation means (for instance, step S02 in an embodiment of the invention which will be described later) which accumulates the current value detected by the current detection unit to obtain an accumulated charging current and an accumulated discharging current and, based on the accumulated charging current and the accumulated discharging current, calculates a remaining charge (for instance, a detected remaining charge SOC in an embodiment of the invention which will be described later) of the power storage unit;
wherein the remaining charge detection device further includes: a no-load state detection unit (for instance, a current consumer releasing unit 23 in an embodiment of the invention which will be described later) which detects a no-load state of the power storage unit; and a remaining charge for calibration calculation unit (for instance, a remaining charge for calibration calculation unit 25 in an embodiment of the invention which will be described later) which calculates, according to the voltage value detected in the no-load state of the power storage unit (for instance, OCV in an embodiment of the invention which will be described later), a remaining charge for calibration (for instance, a remaining charge SOCOCV in an embodiment of the invention which will be described later) with respect to the remaining charge of the power storage unit.
According to the above remaining charge detection device for a power storage unit, the upper limit and the lower limit of the remaining charge of the power storage unit are determined, for instance, from the viewpoint of protecting the power storage unit, so that the remaining charge calculated by the current accumulation method varies within a predetermined range. Also, predetermined map(s) which show the relationships between the temperature, current, and voltage of the power storage unit corresponding to the upper limit and the lower limit of the remaining charge are provided. The maps are constructed based on a stationary state of the power storage unit having no deterioration, e.g., based on the initial state of the power storage unit.
When an internal resistance of the power storage unit increases due to such factors as the deterioration thereof, it may be erroneously determined that the actual remaining charge of the power storage unit has reached the upper limit, which, in fact, it has not, because the detected terminal voltage of the power storage unit has reached the upper limit voltage corresponding to the map of the upper limit remaining charge. According to the present invention, however, a no-load state of the power storage unit is forcibly created by disconnecting the load, such as a motor, from the power storage unit at this stage, and the terminal voltage at the load-release state is measured after a certain period of time. The characteristics of the remaining charge with respect to the terminal voltage at the load-release state are not related to the deterioration of the power storage unit, i.e., the increase in the internal resistance thereof, and they are almost the same as those in a power storage unit having no deterioration, e.g., at the initial state thereof. For this reason, the remaining charge of the power storage unit may be obtained with high accuracy by providing a predetermined relational expression or map which shows the relationship between the terminal voltage and the remaining charge at the load-release state, and by searching the relational expression or map.
In this manner, it becomes possible to calibrate the remaining charge detected at the load-connected state by using the remaining charge which is accurately detected at the load-release state. Accordingly, the remaining charge may be calculated with high accuracy even if the power storage unit is in the load-connected state by setting, for instance, correction coefficients for calibration.
In accordance with another aspect of the invention, the remaining charge detection device for a power storage unit further includes a standard remaining charge calibration unit (for instance, a remaining charge correction unit 22 in an embodiment of the invention which will be described later) which calibrates, based on the remaining charge for calibration calculated by the remaining charge for calibration calculation unit, a predetermined standard remaining charge (for instance, a standard charge SOCf in an embodiment of the invention which will be described later) which may be used when the remaining charge of the power storage unit is expressed as a percentage with respect to the predetermined standard remaining charge.
The present invention also provides a control device for a hybrid vehicle including an engine (for instance, an engine 12 in an embodiment of the invention which will be described later) which outputs a driving force for the hybrid vehicle, a motor (for instance, a motor 11 in an embodiment of the invention which will be described later) which assists an output of the engine in accordance with a driving state of the hybrid vehicle, and a power storage unit which stores energy generated by the motor used as a generator and regenerative energy obtained by the regenerative operation of the motor when the hybrid vehicle decelerates, wherein the control device for a hybrid vehicle includes a remaining charge detection device for the power storage unit, having a current detection unit which detects the current value of a charging current and a discharging current of the power storage unit, a voltage detection unit which detects the voltage value of a terminal voltage of the power storage unit, a current accumulation remaining charge calculation means which accumulates the current value detected by the current detection unit to obtain an accumulated charging current and an accumulated discharging current and, based on the accumulated charging current and the accumulated discharging current, calculates a remaining charge of the power storage unit, a no-load state generation unit (for instance, a current consumer releasing unit 23 in an embodiment of the invention which will be described later) which creates a no-load state for the power storage unit by terminating the output assistance for the engine by the motor and the regenerative operation of the motor; a no-load state detection unit (for instance, also a current consumer releasing unit 23 in an embodiment of the invention which will be described later) which detects the no-load state of the power storage unit; and a remaining charge for calibration calculation unit which calculates, according to the voltage value detected in the no-load state of the power storage unit, a remaining charge for calibration with respect to the remaining charge of the power storage unit.
According to the above control device for a hybrid vehicle, it becomes possible to generate a no-load state of the power storage unit by forcibly creating a state in which the output assistance level and the amount of power regeneration are decreased to zero by inhibiting an output assist operation for the engine by the motor or a regeneration operation of the motor when a hybrid vehicle is decelerated.
In accordance with another aspect of the invention, the current accumulation remaining charge calculation means calculates a remaining charge of the power storage unit while the hybrid vehicle is in a running mode.
In accordance with another aspect of the invention, the control device for a hybrid vehicle further includes a remaining charge correction unit (for instance, a correction determination voltage calculation unit 21 in an embodiment of the invention which will be described later) which retains a predetermined remaining charge (for instance, an upper limit remaining charge SOCMAP and a lower limit remaining charge SOCMAP in an embodiment of the invention which will be described later) that has been set in accordance with a predetermined voltage value (for instance, a voltage value V, an upper limit map voltage value Vmu, or a lower limit map voltage value Vmd in an embodiment of the invention which will be described later), current value (for instance, a current value I in an embodiment of the invention which will be described later), and temperature (for instance, a temperature T in an embodiment of the invention which will be described later) for the power storage unit, the remaining charge correction unit being capable of setting, when the voltage value detected by the voltage detection unit reaches the predetermined voltage value (for instance, the upper limit map voltage value Vmu or the lower limit map voltage value Vmd in an embodiment of the invention which will be described later), the predetermined remaining charge as the remaining charge of the power storage unit, wherein the no-load state generation unit creates the no-load state for the power storage unit when the remaining charge of the power storage unit is corrected by the remaining charge correction unit.
According to the above control device for a hybrid vehicle, a predetermined map for correcting the remaining charge is prepared for correcting the remaining charge calculated by the current accumulation method, and when the condition of the power storage unit is matched with a condition indicated in the map for correcting the remaining charge, a no-load state for the power storage unit may be forcibly generated.
That is, the map for correcting the remaining charge is set for a predetermined remaining charge and, for instance, when the detected value of the terminal voltage of the power storage unit reaches a predetermined voltage value which is set by the map for correcting the remaining charge, a no-load state may be forcibly created in the hybrid vehicle by decreasing the level of output assistance for the engine and the amount of power regeneration to zero. After a certain period of time which is required for stabilizing the no-load state of the power storage unit, the remaining charge of the power storage unit is calculated based on the terminal voltage thereof in the no-load state, and the remaining charge calculated by the current accumulation method is calibrated by using the remaining charge in the no-load state.
In this manner, it becomes possible to avoid stopping the engine output assistance or the regeneration operation of the motor while the vehicle is running, and therefore, to prevent uncomfortableness in driving the vehicle.
In yet another aspect of the invention, the control device for a hybrid vehicle further includes a remaining charge for correction calibration unit (for instance, a remaining charge correction unit 22 in an embodiment of the invention which will be described later) which calibrates the predetermined remaining charge based on the remaining charge for calibration calculated by the remaining charge for calibration calculation unit.
According to the above control device for a hybrid vehicle, the predetermined remaining charge with respect to the remaining charge correction map is calibrated based on the remaining charge in the no-load state. That is, a correction coefficient is calculated based on the remaining charge in the no-load state and the predetermined remaining charge with respect to the remaining charge correction map, and the correction coefficient is applied to, for instance, the voltage value with respect to the remaining charge correction map to renew the remaining charge correction map. For example, for the remaining charge correction map which is set for a predetermined upper limit remaining charge, the correction coefficient may be applied to the upper limit voltage so that the upper limit voltage is increased corresponding to the deterioration of the power storage unit caused by, for instance, the increase in the internal resistance thereof. In this manner, it becomes possible to accurately detect the remaining charge of the power storage unit by, for instance, preventing the detected terminal voltage from reaching the upper limit voltage before the actual remaining charge of the power storage unit reaches the predetermined upper limit remaining charge.
In yet another aspect of the invention, the control device for a hybrid vehicle further includes a standard remaining charge calibration unit (for instance, also the remaining charge correction unit 22 in an embodiment of the invention which will be described later) which calibrates, based on the remaining charge for calibration calculated by the remaining charge for calibration calculation unit, a predetermined standard remaining charge (for instance, a standard charge SOCf in an embodiment of the invention which will be described later) which may be used when the remaining charge of the power storage unit is expressed as a percentage with respect to the predetermined standard remaining charge.
According to the above control device for a hybrid vehicle, when the remaining charge of the power storage unit is expressed as a percentage with respect to the predetermined standard remaining charge, i.e., as a relative value, from the viewpoint of comfortableness in controlling devices, such as a motor or an engine, which are driven by electric power supplied from the power storage unit, a correction coefficient is calculated based on the remaining charge in the no-load state and the predetermined remaining charge with respect to the remaining charge correction map and applied to the standard charge. In this manner, it becomes possible to accurately calculate the remaining charge of the power storage unit regardless of the increase in the internal resistance associated with the deterioration of the power storage unit when, for instance, a remaining charge which is calculated by a current accumulation is expressed as a percentage with respect to the standard charge.
The present invention also provides a hybrid vehicle provided with a remaining charge detection device for a power storage unit. The remaining charge detection device includes a current detection unit which detects the current value of a charging current and a discharging current of a power storage unit; a voltage detection unit which detects the voltage value of a terminal voltage of the power storage unit; and a current accumulation remaining charge calculation means which calculates the accumulation of the current value detected by the current detection unit to obtain an accumulated charging current and an accumulated discharging current and, based on the accumulated charging current and the accumulated discharging current, calculates a remaining charge of the power storage unit. The remaining charge detection device further includes a no-load state detection unit which detects a no-load state of the power storage unit; and a remaining charge for calibration calculation unit which calculates, according to the voltage value detected in the no-load state of the power storage unit, a remaining charge for calibration with respect to the remaining charge of the power storage unit.
In accordance with another aspect of the invention, the remaining charge detection device for a power storage unit of a hybrid vehicle further includes a standard remaining charge calibration unit which calibrates, based on the remaining charge for calibration calculated by the remaining charge for calibration calculation unit, a predetermined standard remaining charge which may be used when the remaining charge of the power storage unit is expressed as a percentage with respect to the predetermined standard remaining charge.